Understanding the Fate of Insensitive Munitions Compounds: Computational Study on Adsorption of Nitroguanidine (NQ) and 1,1-Diamino-2,2-dinitroethylene (FOX7) on Pristine and Al-Hydroxylated α-Alumina Surfaces

Plane-wave density functional theory (DFT) level of investigation was performed on the adsorption of two insensitive munition compounds, nitroguanidine (NQ) and 1,1-diamino-2,2-dinitroethylene (FOX7), on the (0001) surfaces of (4 × 4) Al-terminated α-alumina (α-Al 2 O 3 ) and its Al-hydroxylated form. Surface hydroxylation was obtained by using 16 water molecules. Full geometry optimizations were performed using the vdW-DF2 van der Waals functional. The interaction of electron with core was accounted using the Vanderbilt ultrasoft pseudopotentials. The charge-density difference maps were performed to characterize the nature of munitions adsorption on alumina surfaces. It was revealed that both of the munition compounds will be adsorbed in parallel orientations on alumina surfaces. It was found that deformation energy correction would be required for the reliable interaction energy prediction on pristine alumina surface. On the pristine surface adsorption will be characterized by the covalent type of interaction, while on the Al-hydroxylated surface hydrogen-bonding interaction will take place. Compared with the 2,4,6-trinitrotoluene (TNT), the binding of NQ and FOX7 on alumina surface will be significantly stronger.